The present invention relates generally to a locating table apparatus. More particularly, the present invention relates to the locating table apparatus preferably employed for the purpose of precisely locating a semiconductor producing equipment operable mainly in a clean room.
In general, a conventional locating table apparatus employed in a clean room is constructed such that air in the vicinity of a movable portion such as a ball screw, a ball nut, a linear guide bearing, a support bearing or the like is forcibly sucked by driving, e.g., a vacuum pump to remove dust generated there (fine particles such as abrasion powder, lubricant particles or the like) from the air, the sucked air is caused to pass through an air filter, and the collected dust is then exhausted to the outside so as to maintain the working environment in the duet-free state (refer to e.g., U.S. Pat. No. 4,955,244).
For example, as shown in FIG. 6 which schematically shows the structure of the conventional locating table apparatus, both ends of a screw shaft 20 are rotatably supported by supporting members 32 and 33 fixedly mounted on a base stand 31 in a clean room 30, and a motor 21 is operatively connected to the other end of the screw shaft 20. A nut 25 threadably fitted onto the screw shaft 20 is guided so as to linearly move along a linear guide rail 24b by means of a support member 23 and a linear guide bearing 24a.
A hole 22 is provided on the nut 25 so as to penetrate from the outer surface of the nut 25 to an interior thereof, and a spirally extending exhaust tube 26 is elastically connected to the nut 22 via a nipple (not shown). In detail, the dust generated from the nut 25 is sucked into the exhaust tube 26 by driving an air pump 27, so that the dust is collected in an air filter 28. Subsequently, the clean air removed the dust is caused to recirculate in the clean room 30. The exhaust tube 26 is formed so as to expand and move along a support member 26a. Reference numeral 26b designates a suction piping by way of which the exhaust tube 26 is communicated with the air pump 27.
With the conventional locating table apparatus constructed as described above, when the motor 21 is driven, the nut 25 is axially moved along the screw shaft 20 corresponding to rotational directions of the motor 21. At this time, the duet generated in the vicinity of the nut 25 is sucked into the exhaust tube 26 through the hole 22, so that the dust is collected in the air filter 28.
In addition, the dust density in the clean room 30 is normally monitored by a measuring instrument (dust counter) 34. A controlling device 35 controls the motor 21 such that the motor 21 is driven only when the monitored dust density is higher than a predetermined value. Thus, an environmental servo-system for the clean room 30 is built in the above-described manner.
With the conventional locating table apparatus constructed as described above, although a vacuum method of keeping the dust generating source clean at all times by evacuating is effective to some extent, it is known that various problems are accompanied because of the vacuum piping system as follows.
(1) The air pump, the air filter, the exhaust piping system and so forth occupy a considerably large space inside and outside the table apparatus.
(2) The exhaust piping system are trailed along with the table moving in the forward and rearward directions, so that a new dust generating source arises.
(3) The lower limit of a particle size the dust can be collected in the air filter is definitively determined depending on the mesh size of the air filter.
(4) Even if the linear guide bearing and the linear guiding portion each equipped with a closed type contact seal (e.g., a rubber seal) are cleaned by means of sucking the interior thereof, the cleaning effect obtained is small. In addition, there is a problem that the contact seal itself becomes another dust generating source.